Similar to the current Markdown support, add local preview support for Fountain files, the markup language for screenwriting, (http://fountain.io/) files in Textastic.
As a workaround, you can close the file first and then delete it:
http://www.textasticapp.com/v4/manual/lessons/How_can_I_show_a_list_of_recently_opened_files_How_can_I_close_the_current_file.html
If something is missing on this list, please add a comment and I'll add it as an option.